Two hundred ten patients scheduled for THR were randomized into two groups. Group A (105 patients) received Logiparin (Novo-Nordisk, Denmark) 50 mg/kg body weight once daily, and group B (105 patients) received placebo once daily. Injections started 2 hr preoperatively and continued for 7 days. Blood samples were collected preoperatively before medication and 3 hr after last injection on the seventh postoperative day. Two hundred three patients completed the study: 103 in group A, 100 in group B. In group A there was a significantly higher increase in ASAT (p = 0.0006) and APH (p = 0.0137) compared with group B. Significantly more patients in group A showed an increase from normal preoperative values to pathological postoperative values in ASAT (p = 0.0012) and APH (p = 0.025) compared with group B. All changes were found to be reversible within 2 weeks of termination of drug treatment. Although no conclusion about the mechanism leading to the increase in ASAT and APH is possible from this data, there is very good suggestive evidence that the liver is influenced by this agent.